Help me understand wire sizes from different components to a shared busbar please!

[Dragoth]

I am currently putting together a solar system for my 5th wheel. I have the solar panels installed on the roof and am starting the layout and wiring of the SCC, Busbars, Inverter, etc. I'm having a hard time wrapping my head around the wire sizes.

I have a Victron Power In busbar, a Victron Multiplus II 24/3000/70, and a Victron 150/70 SCC. None of the runs (except the Panels to SCC) will be longer than 10ft. By my understanding, the power output of my SCC is 70A max, so a 6 AWG wire should be sufficient from the SCC to the Busbar (going off the Blueseas wire chart) I am planning on using 4 AWG just because I like to oversize a little. Victron recommends 1/0 wire from the Inverter (I assume that is rated for the draw that could occur from the battery bank?) So I can run 1/0 from the inverter to the busbar and 1/0 from the busbar to the batteries.

What confuses me is that if the inverter needs 1/0 and is connected to the same busbar as the 4 AWG from the SCC, doesn't that subject any wire on the busbar to the same amperage as the largest connection being made? I can't seem to wrap my brain around it and keep thinking that all wires on a connected busbar should be the same size, but then in practice, I rarely see that. Can someone help educate me on this?

Also, when sizing the wire from the panels to the SCC should I be using Isc of the combined array? (In this case, the Isc of one panel is 11.47 so at 3s2p I'd have about 35amps of Isc)

Thanks all for any responses and any help you can be.

 

[corn18]

Current is drawn, not pushed. So the small wires will never see the loads that the big ones are carrying. I have 4/0 inverter wires carrying 325A on the same Lynx as my DC-DC, solar and DC loads. Smallest wire is 8 ga. That 8 ga will never see more than 30A.

And yes to your panel question.

 

[BentleyJ]

It helps if you think about the system in terms of the individual components and how to best protect them from short circuits that would cause excessive heat and potential fire.

For example, 4AWG wire for a 70A charge controller is oversized as you mentioned and the Charge controller is limited as to the current it can deliver. So you would fuse that wire at say 75A but I would place the fuse between the bus bar and the wire coming from the charge controller because the short circuit risk would be the charge controller wiring shorting and potentially getting hundreds of amps from the battery where as the charge controller could never supply that much.

 

[Dragoth]

Current is drawn, not pushed. So the small wires will never see the loads that the big ones are carrying. I have 4/0 inverter wires carrying 325A on the same Lynx as my DC-DC, solar and DC loads. Smallest wire is 8 ga. That 8 ga will never see more than 30A.

And yes to your panel question.

That makes sense and answers my question perfectly. Thank you.

It helps if you think about the system in terms of the individual components and how to best protect them from short circuits that would cause excessive heat and potential fire.

For example, 4AWG wire for a 70A charge controller is oversized as you mentioned and the Charge controller is limited as to the current it can deliver. So you would fuse that wire at say 75A but I would place the fuse between the bus bar and the wire coming from the charge controller because the short circuit risk would be the charge controller wiring shorting and potentially getting hundreds of amps from the battery where as the charge controller could never supply that much.

Good information and basically what I was planning on doing, Thank You!

 

[JRH]

my SCC is 70A max, so a 6 AWG wire should be sufficient

I have found using as big a wire as will “fit” the device, usually rewarded me down the road…

Good luck , you are starting out with good gear.

J.